IGF-1 LR3
Long R3 IGF-1 · Insulin-like Growth Factor 1 Long R3
Long-R3 IGF-1 analog that evades IGFBPs, stretching activity vs native IGF-1. Research analog, not mecasermin (Increlex). Hypoglycemia and mitogenic signaling are the constraints. “3× potency / hyperplasia” is assay and forum language, not a human hypertrophy RCT.
Use-case scores
0–10 against the evidence we have, not a gym ranking. Hidden domains do not apply here.
- Muscle / recomp3.5/10
IGF1R/mTOR biology is real. LR3 is a research analog with long t½. Not Increlex. Mitogenic + hypoglycemia. Community/preclinical: 3.5.
Compound card
- Class
- Long-R3 IGF-1 analog (not mecasermin)
- Formula
- C400H625N111O115S9
- Status
- Not FDA-approved · research use
How it works
IGF-1 LR3 (Long R3 Insulin-like Growth Factor-1) is a modified version of natural IGF-1 with two key changes: a 13-amino-acid extension at the N-terminus and an Arg→Glu substitution at position 3. These modifications dramatically reduce binding to IGF binding proteins (IGFBPs), resulting in a 2-3× increase in biological potency and an extended half-life of ~20-30 hours (vs <15 minutes for native IGF-1).
IGF-1 LR3 activates IGF-1 receptors on muscle cells to promote protein synthesis, nitrogen retention, and glucose uptake. It also promotes satellite cell proliferation, directly supporting muscle hypertrophy. This extended activity window makes precise dosing critical - the receptor is engaged far longer than natural IGF-1.
Source: PMID: 7488657
Background & History
IGF-1 LR3 (Long-Arg3) is a recombinant human IGF-1 with two modifications: a 13-amino-acid N-terminal extension and substitution of glutamic acid with arginine at position 3. These changes reduce binding to IGF-1 binding proteins (which inactivate native IGF-1) by 1000-fold, dramatically extending the active half-life from ~10 minutes to 20-30 hours. Developed for research use, it allows prolonged direct cellular IGF-1 receptor stimulation without the binding protein "buffering" that limits native IGF-1.
Research Use Cases
- ✓Identity: LR3 vs DES vs mecasermin
- ✓Hypoglycemia and mitogenic signaling as constraints
- ✓Not a hyperplasia guarantee
Dosing
| Phase | Dose | Frequency | Notes |
|---|---|---|---|
| Starting Dose | 20 - 40 mcg | Post-workout (IM or SC) | Start at the low end. Monitor blood glucose closely. 20-40 mcg post-workout for 4 weeks max. |
| Standard Protocol | 40 - 60 mcg | Post-workout - 4 weeks on / 4 weeks off | Always cycle - receptor desensitization occurs with continuous use. Maximum 100 mcg/day. |
Administration
Timeline
Who it is for
Muscle Hypertrophy
HighMost potent peptide for direct muscle protein synthesis and satellite cell proliferation. Requires careful use.
Fat Loss
ModerateImproves nutrient partitioning - carbohydrates preferentially stored as muscle glycogen rather than fat.
Reconstitution
| Vial | Water | Concentration | Example dose |
|---|---|---|---|
| 1 mg lyophilized | 1 mL BAC | 1 mg/mL | 20 mcg on 1 mg / 1 mL = 0.02 mL = 2 units on a U-100. Tiny volumes; use an insulin syringe and respect hypoglycemia. |
Change vial size or water volume? Open the reconstitution calculator.
Safety & Considerations
Research peptide - not FDA-approved. Risk of hypoglycemia (monitor blood glucose, have fast carbs available). May promote growth of existing tumors. Do not exceed 100 mcg/day. Cycle strictly - 4 weeks on / 4 off. Do not combine with insulin.
Regulatory & Legal Status
Competitive athletes subject to anti-doping controls should not use IGF-1 LR3.
Research Chemical
US Compounding: Not eligible / not available
⚠️ This information is for educational purposes only and may not reflect the most current regulatory updates. Always verify with official FDA, WADA, and jurisdiction-specific sources before use.
Limits of current evidence
- “3× native IGF-1” is assay language, not a human hypertrophy RCT.
- Do not stack freely with insulin. Same receptor family.
- This site will not treat wasting or GHD from an LR3 page.
Verdict
IGF-1 LR3 is a binding-protein-evasive IGF-1 analog. Mecasermin is the approved native IGF-1 product. This leaf is not that. Hypoglycemia and mitogenic signaling are the adult constraints, not a hyperplasia guarantee.
Interactions & Contraindications
Hypoglycemia risk is significant - always inject post-workout with carbohydrates available. Do not use with active cancer (strong mitogenic signal). Monitor with insulin - risk of compounded hypoglycemia. Localized fat at injection site if injected in same area repeatedly.
Synergies & Common Stacks
Ipamorelin raises endogenous GH (which then creates IGF-1 in the liver); IGF-1 LR3 directly stimulates the tissue receptor. Dual-pathway IGF-1 pathway activation.
BPC-157 drives VEGF/angiogenesis at repair sites; IGF-1 LR3 provides the anabolic mTOR signal for new tissue synthesis. Full regenerative stack.
IGF-1 LR3 vs. MK-677
Canonical comparison: IGF-1 LR3 vs MK-677
| Attribute | IGF-1 LR3 | MK-677 |
|---|---|---|
| Administration | Subcutaneous injection | Oral (daily) |
| Mechanism | Direct IGF-1 receptor agonist | Ghrelin receptor agonist → GH → IGF-1 |
| IGF-1 Elevation | Direct, immediate, strong | Indirect - GH stimulation cascade |
| Half-Life | 20–30 hours (LR3 modification) | 24-hour sustained oral action |
| Muscle Uptake | Direct muscle anabolic signaling | Systemic GH/IGF-1 elevation |
| WADA Status | Prohibited (S2) | Prohibited (S2) |
Verdict: IGF-1 LR3 offers direct, potent anabolic signaling at the receptor level - typically stronger for muscle hypertrophy than MK-677. However, MK-677 also provides GH itself (bone density, sleep, recovery) via the indirect GH cascade.
Frequently Asked Questions
What is the difference between IGF-1 LR3 and regular IGF-1?▼
Does IGF-1 LR3 cause hypoglycemia?▼
References
- Adams GR “"IGF-1 LR3 and skeletal muscle growth".” Exercise and Sport Sciences Reviews (2002). PMID: 12150568
- Samani AA, et al. “Insulin-like growth factor-I (IGF-I) and its receptor in health and disease.” Endocr Rev (2007). PMID: 17409286
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